Let me explain why this happens so the other users know as well
You have clicked on the "Renew" button, which has generated a new invoice.
Then you have added the promo code in this invoice.
Then, for some reason, you have left the Checkout page. But the generated invoice is still in the system and the promo code is marked as used.
So, if you try to renew again, another invoice will be generated but the promo code will no longer be valid for you (as it is being used in the previous invoice, even though it has not been paid).
Anyway, the solution is that I delete the invoice that you have created (where you have added the promo code).
I just did it so you should be able to use the promo code again (in only one invoice!)